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Abstract:

Multiple alignment patterns, each composed of first and second alignment
pattern elements printed by forward and backward movements of a print
head, respectively, are formed while the relative printing positions of
the two elements are shifted. From optical characteristics data thereof,
whether the data is influenced by a disturbance is determined. When the
data is determined to be less influenced by the disturbance and therefore
to be reliable, an adjusting value for aligning positions in printing in
reciprocal movements is calculated by use of: data with the smallest
relative printing position misalignment between the first and second
alignment pattern elements; and data of optical characteristics close to
the data. When the data is largely influence by the disturbance, a range
of shifting of relative position is widened than that of the data less
influenced by the disturbance so that more data pieces are used to obtain
the adjusting value.

Claims:

1-10. (canceled)

11. A printing position alignment method for aligning printing positions
by first and second printing operations, comprising: a printing step of
printing a plurality of alignment patterns, each alignment pattern being
composed of a first alignment pattern element printed by the first
printing operation and a second alignment pattern element printed by the
second printing operation, and the plurality of alignment patterns being
printed by shifting the relative printing position of the second
alignment pattern element relative to the first alignment pattern
element; a measuring step of measuring the respective optical
characteristics of the plurality of alignment patterns; a plotting step
of plotting data of the respective optical characteristics of the
plurality of alignment patterns on coordinates; and a determining step of
determining a number of data in accordance with a result of plotting by
the plotting step to obtain an approximate curve, and determining an
adjusting value of the second printing operation relative to the first
printing operation.

12. A printing position alignment method as claimed in claim 11, wherein,
in the determining step, the approximate curve is obtained in accordance
with the smaller number of data in a case where reliability of the result
of plotting by the plotting step is relatively higher than a case where
the reliability of the result is relatively low.

13. A printing position alignment method as claimed in claim 11, wherein
the first and second printing operations are performed by an operation in
which different printing elements each print for either of the first and
second printing operations while moving relative to a printing medium.

14. A printing position alignment method as claimed in claim 11, wherein
the first and second printing operations are performed by an operation in
which the printing of the same printing element is performed for both the
first and second printing operations while reciprocating relative to the
print medium.

15. A printing position alignment method as claimed in claim 11, wherein
an inkjet printing head that ejects ink for performing the first and
second printing operations is used.

16. A printing position alignment method as claimed in claim 15, wherein
the optical characteristic is a density of ink printed on a print medium.

17. A printing apparatus that performs first and second printing
operations, comprising: a controller which makes print a plurality of
alignment patterns, each alignment pattern being composed of a first
alignment pattern element printed by the first printing operation and a
second alignment pattern element printed by the second printing
operation, and the plurality of alignment patterns being printed by
shifting the relative printing position of the second alignment pattern
element relative to the first alignment pattern element; a measuring unit
which measures the respective optical characteristics of the plurality of
alignment patterns; a plotting unit which plots data of the respective
optical characteristics of the plurality of alignment patterns on
coordinates; and a determining unit which determines a number of data in
accordance with a result of plotting by the plotting step to obtain an
approximate curve, and determines an adjusting value of the second
printing operation relative to the first printing operation.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a printing position alignment
method in dot matrix printing, and a printing apparatus using the method.

[0003] 2. Description of the Related Art

[0004] One type of printing apparatuses performing printing by forming
dots on a printing medium uses a print head that moves in a predetermined
direction relative to a printing medium and has, as printing elements,
ink ejection openings arranged in a direction (e.g., in a direction in
which a printing medium is conveyed) different from the predetermined
direction. Nowadays, as for such a printing apparatus (an inkjet printing
apparatus), there is a trend of increasing the number of ejection
openings arranged in a print head to achieve a higher printing speed.
Furthermore, increasingly widely used is a print head provided with
multiple arrays of ejection openings corresponding to multiple ink colors
so as to perform color printing. Particularly, the number of ink colors
is increased in order to improve print quality, and not only cyan,
magenta, yellow and black to reproduce a full color image but also inks
in other color tone (color and density) are also increasingly used. For
example, in some cases, light color inks are used to reduce a granular
impression stemming from ink dots formed on a printing medium, or
particular color inks such as red, blue and green are used to increase a
color reproduction range.

[0005] Under the above circumstances, with the increase of the number of
arrays of ejection openings formed in a print head, a misalignment of dot
printing positions among arrays of ejection openings is more likely to
occur due to a variation among ejection opening formation positions
occurring at the time of manufacturing of a print head; a displacement of
an attachment position of a print head; or the like. Further, also in a
case of use of multiple print heads, a misalignment of dot printing
positions may occur due to a relative position displacement among the
print heads. In addition, even the same ejection openings may cause a
misalignment between dot printing positions when performing printing
(bi-directional printing) by reciprocal movement of the print head in
both directions. When the misalignments of these dot printing positions
occur as described above, print quality is deteriorated. One of
heretofore-known technique for solving this problem is to perform a
process of adjusting the dot printing positions by correcting the
forgoing misalignments of dot printing positions (hereinafter, referred
to as a registration process).

[0006] The registration process can be carries out in such a way that a
certain array of ejection openings is determined as a reference array;
the relative position misalignment between dots printed by the reference
ejection opening array and dots printed by the other ejection opening
array is obtained; and timing of ejecting inks is corrected based on the
relative position misalignment. It is also possible to perform the
registration process on misalignments of dot printing positions between a
forward movement and a backward movement in bi-directional printing, by
correcting the ejection timing in the same fashion.

[0007] The following method is cited as a method for obtaining an
adjusting value to align dot printing positions. The method uses an array
of ejection openings as a reference array and another array of ejection
openings as an adjustment target array, and involves: printing multiple
sample patterns (hereinafter, referred to as alignment patterns), while
changing the ejection timing of the adjustment target array of ejection
openings for each sample pattern; and then obtaining the adjusting value
through a user's visual check on the sample patterns. Similarly, in a
case of obtaining an adjusting value for dot print alignment in
bi-directional printing, this method also involves: printing multiple
alignment patterns while making the ejection timing in a backward
movement differ from the ejection timing in a forward movement for each
sample pattern; and providing the multiple alignment patterns to a user's
visual check. In other words, the user selects a pattern in which a dot
printing position is best matched, from among the multiple alignment
patterns printed on a printing medium, and inputs its information to set
an adjusting value for the printing apparatus.

[0008] However, this method forces a user to perform a complex operation
of a visual judgment or a selection setting.

[0009] In addition, improving an alignment accuracy requires an increase
of the number of alignment patterns, so that the user needs to correctly
judge small differences in misalignments of ink landed positions.

[0010] Therefore, in some cases, an alignment method is employed (e.g.,
Japanese Patent Application Laid-Open No. 10-329381 (1998)) in which a
sensor is mounted on a carriage of an inkjet printing apparatus, and is
caused to scan a printing medium so as to optically read alignment
patterns, whereby the inkjet printing apparatus automatically determines
an adjusting value.

[0011] Recently, the droplet size of ejecting ink has become smaller for
improvement of image quality. Accordingly, an influence of an external
disturbance on ink ejection or dot printing has become larger. The
external disturbance includes, for example, a vibration occurring when a
carriage with a print head mounted thereon moves, a change of the
attitude of a print head in scanning due to distortion of a rail stay
supporting the carriage, or waves (cockling) of a printing medium
occurring when a pattern is printed on the printing medium. These
external disturbances each not only act as a factor of a change in dot
printing positions in printing of an alignment pattern, but also give an
impact, if an automatic alignment is employed, on optical characteristics
obtained by reading the alignment patterns with an optical sensor mounted
on a carriage. In particular, in the case of an ink whose optical
characteristic of alignment patterns is originally difficult to detect,
like the light color ink described above, the optical sensor can only
output data with a low S/N ratio, so that such ink is particularly
susceptible to an influence of the external disturbance.

[0012] Possible countermeasures to check these external disturbances are
to improve a mechanical accuracy of a printing apparatus, and to limit
types of printing media for printing an alignment pattern thereon for an
automatic alignment, to a type of printing medium enabling easy optical
detection. However, these countermeasures are not desirable in terms of
cost and usability. Therefore, it is strongly desired to determine an
adjusting value with a certain degree of accuracy, even when an
optically-read output value of an alignment pattern is influenced by an
external disturbance.

[0013] As a prior art to meet such a demand, one disclosed in Japanese
Patent Application Laid-Open No. 2006-102997 is cited. This document
employs a method including: printing a pattern for abnormal detection in
synchronization with alignment patterns; and correcting an output value
obtained by reading an alignment pattern influenced by an external
disturbance in alignment processing, or calculating an adjusting value by
excluding an influenced pattern in calculating the adjusting value.

[0014] However, according to Japanese Patent Application Laid-Open No.
2006-102997, it is necessary to print the pattern for abnormal detection
in addition to alignment patterns. Therefore, there are problems left
that the performing of a registration process needs a long time; the
printing of the pattern for abnormal detection accordingly increases an
amount of ink to be consumed, and in some cases, increases an amount of
printing media, i.e., requires more resources to be consumed.

SUMMARY OF THE INVENTION

[0015] An object of the invention is to enable an effective and automatic
registration process which uses only a small amount of resources such as
ink and printing media, while reducing an impact of an external
disturbance.

[0016] In a first aspect of the present invention, there is provided a
printing position alignment method for aligning printing positions by
first and second printing operations, comprising: a printing step of
printing a plurality of alignment patterns, each alignment pattern being
composed of a first alignment pattern element printed by the first
printing operation and of a second alignment pattern element printed by
the second printing operation, the each alignment pattern indicating a
different optical characteristic due to a misalignment in a relative
printing position of the second alignment pattern element relative to the
first alignment pattern element, and the plurality of alignment patterns
being printed by shifting the relative printing position of the second
alignment pattern element relative to the first alignment pattern
element; a measuring step of measuring the respective optical
characteristics of the plurality of alignment patterns;

[0017] a determination step of determining reliability of the plurality of
alignment patterns based on, among data of the plurality of optical
characteristics thus measured, data indicating that a misalignment of the
relative printing position of the second alignment pattern element to the
first alignment pattern element is smallest and data of optical
characteristics in the neighborhood of the data indicating the smallest
misalignment; and an adjusting value obtaining step of, in a case where
the reliability is determined to be high in the determination step,
obtaining an adjusting value for aligning the printing positions based on
a smaller number of pieces of data of the optical characteristics than
that in the case where the reliability is determined to be low.

[0018] In a second aspect of the present invention, there is provided a
printing position alignment method for aligning printing positions by
first and second printing operations, comprising: a printing step of
printing a plurality of first alignment patterns, each first alignment
pattern being composed of a first alignment pattern element printed by
the first printing operation and of a second alignment pattern element
printed by the second printing operation, the each first alignment
pattern indicating a different optical characteristic due to a
misalignment in a relative printing position of the second alignment
pattern element relative to the first alignment pattern element, and the
plurality of first alignment patterns being printed by shifting the
relative printing position of the second alignment pattern element
relative to the first alignment pattern element; a measuring step of
measuring the respective optical characteristics of the plurality of
alignment patterns; a determination step of determining reliability of
the plurality of the first alignment patterns based on, among data of the
plurality of optical characteristics thus measured, data indicating that
a misalignment of the relative printing position of the second alignment
pattern element to the first alignment pattern element is smallest and
data of optical characteristics in the neighborhood of the data
indicating the smallest misalignment; and an adjusting value obtaining
step of, in a case where the reliability is determined to be low in the
determination step, obtaining an adjusting value for aligning the
printing positions based on data of the plurality of optical
characteristics, and in a case where the reliability is determined to be
high in the determination step, printing a plurality of second alignment
patterns different from the first alignment patterns, measuring
respective optical characteristics of the second alignment patterns thus
printed, and obtaining an adjusting value for aligning the printing
position on the basis of data of the plurality of optical characteristics
of the second alignment patterns thus measured.

[0019] In a third aspect of the present invention, there is provided a
printing apparatus that performs first and second printing operations and
capable of aligning printing positions by the first and second printing
operations, comprising: a controller which makes print a plurality of
alignment patterns, each alignment pattern being composed of a first
alignment pattern element printed by the first printing operation and of
a second alignment pattern element printed by the second printing
operation, the each alignment pattern indicating a different optical
characteristic due to a misalignment in a relative printing position of
the second alignment pattern element relative to the first alignment
pattern element, and the plurality of alignment patterns being printed by
shifting the relative printing position of the second alignment pattern
element relative to the first alignment pattern element; a measuring unit
which measures the respective optical characteristics of the plurality of
alignment patterns; a determination unit which determines reliability of
the plurality of alignment patterns based on, among data of the plurality
of optical characteristics thus measured, data indicating that a
misalignment of the relative printing position of the second alignment
pattern element to the first alignment pattern element is smallest and
data of optical characteristics in the neighborhood of the data
indicating the smallest misalignment; and an adjusting value obtaining
unit, in a case where the reliability is determined to be high by the
determination unit, which obtains an adjusting value for aligning the
printing positions based on a smaller number of pieces of data of the
optical characteristics than that in the case where the reliability is
determined to be low.

[0020] In a fourth aspect of the present invention, there is provided a
printing apparatus that performs first and second printing operations and
capable of aligning printing positions by the first and second printing
operations, comprising: a controller which makes print a plurality of
first alignment patterns, each first alignment pattern being composed of
a first alignment pattern element printed by the first printing operation
and of a second alignment pattern element printed by the second printing
operation, the each first alignment pattern indicating a different
optical characteristic due to a misalignment in a relative printing
position of the second alignment pattern element relative to the first
alignment pattern element, and the plurality of first alignment patterns
being printed by shifting the relative printing position of the second
alignment pattern element relative to the first alignment pattern
element; a measuring unit which measures the respective optical
characteristics of the plurality of alignment patterns; a determination
unit which determines reliability of the plurality of the first alignment
patterns based on, among data of the plurality of optical characteristics
thus measured, data indicating that a misalignment of the relative
printing position of the second alignment pattern element to the first
alignment pattern element is smallest and data of optical characteristics
in the neighborhood of the data indicating the smallest misalignment; and
an adjusting value obtaining unit which, in a case where the reliability
is determined to be low by the determination unit, obtains an adjusting
value for aligning the printing positions based on data of the plurality
of optical characteristics, and in a case where the reliability is
determined to be high by the determination unit, prints a plurality of
second alignment patterns different from the first alignment patterns,
measures respective optical characteristics of the second alignment
patterns thus printed, and obtains an adjusting value for aligning the
printing position on the basis of data of the plurality of optical
characteristics of the second alignment patterns thus measured.

[0021] In the invention, it is determined whether from data of optical
characteristics of respective alignment patterns, the data are influenced
by a disturbance. When the influence of the disturbance is small so that
the data are reliable, a piece of data in which a misalignment of a
relative printing position of the second alignment pattern elements to
the first alignment pattern elements is smallest and data of optical
characteristics in the neighborhood of the piece of data are used so that
an adjusting value is calculated. In such a range, a change of density to
relative shifting amount of printing position is obtained as a simple
function so that an adjusting value can be determined with high accuracy.
Meanwhile, when the influence of the disturbance is large, a range of an
amount of shifting of a relative position is made wider than that in the
case where the influence of the disturbance is small, a large number of
pieces of data of optical characteristics are used. Thus, since a change
of optical characteristics (density) becomes large, a ratio of the
disturbance to a density curve is reduced, and an increase of the number
of pieces of data to be used is capable of improving the reliability of
an adjusting value.

[0022] As described above, in accordance with the invention, when
performing an automatic registration process, it becomes possible to
improve the efficiency of the process and reduce an amount of resource
such as ink and printing media as much as possible, with the influence of
a disturbance being reduced.

[0023] Further features of the present invention will become apparent from
the following description of exemplary embodiments (with reference to the
attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a perspective view showing a basic configuration example
of an inkjet printing apparatus to which the invention is applicable;

[0025] FIG. 2A is an exploded-perspective view of an inkjet cartridge of
the inkjet printing apparatus of FIG. 1, and FIG. 2B is an enlarged
perspective view of an ejection opening array of the inkjet cartridge;

[0026] FIG. 3 is a schematic view of an optical sensor mounted on the
inkjet printing apparatus of FIG. 1;

[0027]FIG. 4 is a block diagram showing a configuration example of a
control system of the inkjet printing apparatus of FIG. 1;

[0028] FIGS. 5A to 5C are each an example of alignment patterns applicable
to a first embodiment of the invention, which example is composed of two
complementary alignment pattern elements;

[0029] FIGS. 6A to 6C are each another example of alignment patterns
applicable to the first embodiment of the invention, the example being
composed of two alignment pattern elements disposed in the same position;

[0030]FIG. 7 is a flowchart according to the first embodiment of the
invention, the flowchart showing an example of a procedure for
calculating an adjusting value by combining to density data with multiple
reliability determination methods;

[0031] FIG. 8 shows some examples of density data and approximation curves
in order to explain an application of the reliability determination
methods of the first embodiment of the invention; and

[0032]FIG. 9 is a flowchart showing a process procedure of a second
embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

[0033] The invention is described in detail below with reference to the
drawings.

Basic Configuration Example of Inkjet Recording Apparatus

[0034] FIGS. 1 to 4 are views showing a basic configuration example of an
inkjet printing apparatus to which the invention is applicable.

[0035]FIG. 1 is a perspective view showing a configuration example of a
color inkjet printing apparatus to which the invention is applicable, and
shows a state in which a front cover is removed to expose the inside of
the apparatus.

[0036] In FIG. 1, reference numeral 1000 denotes a replaceable inkjet
cartridge, and reference numeral 2 denotes a carriage unit for detachably
holding the inkjet cartridge 1000. Reference numeral 3 denotes a holder
fastening the inkjet cartridge 1000 to the carriage unit 2. When a
cartridge fastening lever 4 is operated after the inkjet cartridge 1000
is mounted into the carriage unit 2, the inkjet cartridge 1000 is brought
into contact with the carriage unit 2 by pressuring. Due to this contact,
the inkjet cartridge 1000 is positioned and, at the same time, an
electric contact for signal transmission provided to the carriage unit 2
is connected with an electric contact on the side of the inkjet cartridge
1000. Reference numeral 5 denotes a flexible cable through which an
electric signal is transmitted to the carriage unit 2.

[0037] Further, while not shown in FIG. 1, in an automatic registration
process system, the carriage unit 2 is provided thereon with a reflection
type optical sensor (described later) which serves as a function to
detect printing densities of a plurality of alignment patterns printed on
a printing medium. A conveyance of a printing medium in an arrow Y
direction and a movement of the carriage unit 2 to which the optical
sensor is attached in an arrow X direction, are alternately performed,
whereby densities of a group of alignment patterns printed on the
printing medium can be detected. This optical sensor may also be used as
a detection unit for detecting an edge of the printing medium.

[0038] Reference numeral 6 denotes a carriage motor which reciprocates the
carriage unit 2 in the X direction as a drive source, and reference
numeral 7 denotes a carriage belt which transmits power of the carriage
motor 6 to the carriage unit 2. Reference numeral 8' denotes a guide
shaft, extending in the X direction, which supports and guides the
carriage unit 2 to allow the carriage unit 2 to move in the X direction.
Reference numeral 9 denotes a transmission type photo coupler attached to
the carriage unit 2, and reference numeral 10 denotes a light shielding
plate disposed in a vicinity of a predetermined carriage home position.
Reference numeral 12 denotes a home position unit including a recovering
system such as a capping member which caps a face (ejection face) of an
inkjet print head on which ejection openings are formed, a suction unit
which sucks this capping member, a member wiping the ejection face of the
print head, and the like.

[0039] Reference numeral 13 denotes a discharge roller for discharging a
printing medium. The discharge roller holds a printing medium between
itself and an unillustrated spur-like roller in cooperation to discharge
the printing medium to the outside of the printing apparatus. Reference
numeral 14 denotes a line feed unit which conveys a printing medium in
the Y direction by a predetermined amount.

[0041] Reference numeral 15 denotes an ink tank storing a black (Bk) ink,
and reference numeral 16 denotes an ink tank storing inks of cyan (C),
magenta (M), and yellow (Y). These ink tanks are detachable to an inkjet
cartridge main body. Reference numeral 17 denotes connection openings on
the ink tank 16 side, which openings correspond to ink supply tubes 20 on
the inkjet cartridge main body side to introduce the respective inks
stored in the ink tank 16 thereto. Reference numeral 18 denotes
connection openings on the ink tank 15 side, which correspond to ink
supply tubes on the inkjet cartridge main body side to introduce the
black ink stored in the ink tank 15 thereto. The connection openings 17,
18 are connected with the corresponding ink supply tubes on the inkjet
cartridge main body side, and the connection enables a supply of ink to
the print head 1 held in the inkjet cartridge main body. Reference
numeral 19 denotes an electric contact portion, and connection with the
electric contact portion disposed on the carriage unit 2 enables a
receipt of an electric signal from a controller of the main body of the
printing apparatus via the flexible cable 5.

[0042] In this example, used is the print head 1 including a black ink
ejection opening array 1A with ejection openings disposed to eject black
ink, and a color ink ejection opening array 1B. These arrays are disposed
in parallel with each other. In the color ink ejection opening array 1B,
a group of ejection openings for ejecting Y, M, and C is integrally
formed in an in-line fashion, and is disposed in parallel with the black
ink ejection opening array 1A.

[0043]FIG. 2B is a schematic perspective view showing a fragment of a
main-portion structure of the print head 1 of the inkjet cartridge 1000.

[0044] In each ejection opening array of the print head 1, a plurality of
ejection openings 22 are formed at predetermined pitches on the ejection
face 21 facing a printing medium with a gap (e.g., approximately 0.5 mm
to 2.0 mm) interposed therebetween. An electrothermal transducer element
(a heating resistor or the like) 25 is provided along a wall surface of
each liquid passage 24 communicating the ejection opening 22 and a common
liquid chamber 23, and generates thermal energy for ink ejection. The
inkjet cartridge 1000 of this example is mounted on the carriage unit 2
so that the ejection openings 22 of each ejection opening array are
aligned in a direction crossing the moving direction of the carriage unit
2 (for example, in the direction of conveying a printing medium).
Further, the electrothermal transducer elements 25 corresponding to an
image signal or an ejection signal are driven to boil an ink in the
liquid passage 24 into film-boiling. At this time, pressure induced by
bubbles thus generated causes the ink to be ejected through the ejection
openings 22.

[0045] FIG. 3 is a schematic view for explaining a reflection type optical
sensor mounted on the carriage unit 2.

[0046] A reflection type optical sensor 30 includes a light emitter 31 and
an optical receiver 32. Light beam 35 emitted from the emitter 31 is
reflected on a printing medium 8, and a reflected light beam 37 is
detected by the optical receiver 32. A detection signal of the optical
receiver 32 is transmitted to an electric board of the printing apparatus
as information. In order to detect densities of a group of alignment
patterns printed on the printing medium 8 in such a manner that the
detected densities are equal to those viewed by a person, a configuration
for detecting a diffusion light is made by use of different light angles
between incidence and reflection.

[0047] In this example, considering that inks of the respective colors, C,
M, Y, and black are used in a registration process, a white LED or a
three primary color LED is used for the light emitter 31, and a
photodiode having sensitivity for visible light is used for the optical
receiver 32. When ink dots of two different colors are targets for
alignment, it is preferable that a three primary color LED be used for
the light emitter 31 since the three primary color LED is capable of
selecting and emitting a color with high sensitivity for alignment
patterns printed with the two different colors.

[0048]FIG. 4 is a block diagram showing a diagrammatic configuration
example of a control system of the printing apparatus.

[0049] In FIG. 4, a CPU 100 performs a control process of operation of the
printing apparatus, a data process, and the like including processes to
be described later with reference to FIG. 7 or FIG. 9. A ROM 101 stores
therein programs such as procedures for the above, and a RAM 102 is used
as a work area or the like for performing these processes. Reference
numeral 110 denotes a nonvolatile memory such as an EEPROM, which stores
therein required information even when the apparatus is turned off.

[0050] The ejection of ink from the print head 1 is performed by supplying
drive data (image data) and drive control signal (a heat pulse signal) to
a head driver 1A, which supply is performed by the CPU 100. The CPU 100
controls a carriage motor 103 for driving the carriage in the X direction
of FIG. 1 via a motor driver 103A, and also controls a conveying motor
104 for conveying a printing medium in the Y direction of FIG. 1 via a
motor driver 104A.

[0051] In addition, as will be described later, the CPU 100 performs an
alignment process (registration process) for a printing position by
utilizing an optical sensor 30. A function of this alignment process may
be performed on a host device 200 side which supplies image data to the
printing apparatus. An obtained adjusting value may also be stored in the
host device 200.

Recording Alignment Pattern

[0052] In the registration process of this embodiment, a plurality of
alignment patterns are first printed on a printing medium. At this time,
alignment patterns are each composed of a first alignment pattern element
printed by a first printing operation and a second alignment pattern
element printed by a second printing operation, but printing positions of
the second alignment pattern elements relative to the first alignment
pattern elements are different from each other. Determination of arrays
of ejection openings used for forming the first and second alignment
pattern elements on the first and second printing operations depends on
the combination of ink colors of an alignment target and moving
directions.

[0053] An example of this combination will be described. In this example,
there are provided ejection opening array 1A for black ink and ejection
opening array 1B for color inks. In alignment in the case where the
carriage moves in a forward direction, a reference array (for example,
the ejection opening array for black ink) is determined from among these
arrays to print a group of first alignment pattern elements, while a
group of second alignment pattern elements is printed by the other
ejection opening array (for example, the ejection opening array for color
inks). Alignment in the carriage movement in the backward direction is
performed in the same manner. Further, when the number of ejection
opening arrays is three or more, a plurality of groups of alignment
patterns may be printed depending on the number of combinations of a
reference ejection opening array and each of the other ejection opening
arrays. In addition, concerning alignment patterns for the alignment of
bi-directional printing, only the reference ejection opening array is
used, and a group of first alignment pattern elements and a group of
second alignment pattern elements are printed in a forward directional
movement and a backward directional movement of the carriage,
respectively.

[0054] In any case, relative printing positions of the second alignment
pattern elements to the first alignment pattern element are different.
The number of alignment patterns or of elements thereof can be determined
depending on a unit of shifting of a relative printing position required
for satisfying a requirement of an accuracy of the registration process
and depending on an alignment range required based on a mechanical
tolerance of an apparatus. A printing area of alignment patterns can be
optimized with respect to the size of a printing medium to be used for
alignment pattern printing and the throughout of alignments, on the basis
of the size of a detection area of an optical sensor, a range of width in
which printing is possible in one movement of the carriage, the size of
the printable area of a printing medium for a group of alignment
patterns, and the like.

[0055] Alignment patterns are printed so that a change of an optical
characteristic, i.e., a change of density, occurs in proportion to a
shifting amount of a relative printing position of the second alignment
pattern element to the first alignment pattern element.

[0056] FIGS. 5A to 5C are each a schematic view of an alignment pattern A
composed of first and second alignment pattern elements A1 and A2.

[0057] In FIGS. 5A to 5C, dots depicted by black circles represent ink
dots of the first alignment pattern element A1. Dots depicted by white
circles represent ink dots of the second alignment pattern element A2. In
FIGS. 5A to 5C, although black and white dots are used for the sake of
description only, this is not intended to represent colors and densities
of inks.

[0058]FIG. 5A is an explanatory view of a state in which printing
positions of the first and second alignment pattern elements A1 and A2
are aligned with each other. FIG. 5B shows a state in which printing
positions of both elements are slightly misaligned from each other, and
FIG. 5C shows a state in which printing positions of both elements are
further misaligned from each other.

[0059] A group of alignment patterns A of this example is set so that
densities of all alignment patterns are reduced as a misalignment of
printing positions between the first and second alignment pattern
elements A1 and A2 increases. That is, in FIG. 5A, an area factor covered
with dots is approximately 100%. Further, as shown in FIGS. 5B and 5C, as
a misalignment of the printing positions increase, an amount of overlap
between the first A1 and second alignment pattern elements A2 also
increases, so that an area on which printing is not performed, i.e., an
area which is not covered with dots, develops.

[0060] That is, an object of the groups of alignment patterns is to cause
the area factor to be reduced as the relative printing positions of the
second alignment pattern elements A2 to the first alignment pattern
elements A1 are misaligned to a larger extent. Printing density depends
strongly on the area factor. Therefore, an increase of an area with no
printing influences more on entire density than an increase of density
due to overlaps of dots does. Accordingly, based on a change of density
obtained by the reading of a group of alignment patterns by the optical
sensor 30, and based on a condition of a relative printing position in
the case where density is highest, an adjusting value can be obtained.

[0061] In addition, as the disposition of alignment patterns, as shown in
the examples of FIGS. 5A to 5C, the first and second alignment pattern
elements may be disposed on different regions, respectively, in the X
direction (left and right directions in FIGS. 5A to 5C) of FIG. 1, or may
be disposed on the same region.

[0062] FIGS. 6A to 6C show an example of an alignment pattern B in which
dots are disposed on the same positions in the X direction. In the
example shown in the drawings, for the sake of convenience, dots
composing a first alignment pattern element B1 and a second alignment
pattern element B2 are depicted so that the dots do not overlap each
other in a conveying direction (upward and downward directions in FIGS.
6A to 6C), but in practice, the dots may overlap each other in conveying
direction, which causes no problem. In this example, in a state (FIG. 6A)
printing positions are aligned, since an area in which dots are disposed
is small and the area factor is small, density is reduced. In FIG. 6B in
which printing positions are misaligned, the positions of dots of the
first and second alignment pattern elements B1 and B2 are misaligned
whereby the area factor is increased, so that density is increased. As in
FIG. 6C, when the printing positions are further misaligned, density is
further increased.

[0063] As shown in the above two examples, the point is that, on condition
that an area factor or density sensitively changes depending on
magnitudes of misalignments of the first and second alignment pattern
elements, appropriate alignment patterns can be employed.

Reading Alignment Pattern

[0064] Groups of alignment patterns printed in the above manner are
scanned by the optical sensor 30, which is mounted on the carriage unit 2
and includes a white LED or a three primary color LED of RGB and a photo
diode, so that optical characteristic (density) is measured. For the LED
to be used, a color having the highest detection efficiency is selected
for each ink to be measured. A signal detected by the optical sensor 30
is transmitted to an unillustrated A/D converter, and thereby, a
converted signal is stored in a RAM 102 as a density data value of a read
alignment pattern.

[0065] The optical sensor 30 only needs to have a detection capability
good enough to obtain a density difference among multiple alignment
patterns each composed of two alignment pattern elements, and does not
necessarily have a detection capability good enough to detect an absolute
value of the densities. Further, the optical sensor 30 preferably has
resolutions which can be used for detection in a narrower range than a
range on which a single alignment pattern is printed.

Calculation of Alignment Value

[0066] An adjusting value for a registration process is calculated by use
of pattern density read by the optical sensor 30 and a shifting amount xi
(i denotes a number allocated to each alignment pattern) of a relative
position of a second alignment pattern element to a first alignment
pattern element set with respect to each alignment pattern.

[0067] FIG. 8 show examples of distributions of density with respect to
shifting amounts of relative positions. A position where printed dots of
two alignment pattern elements correctly aligned each other is a position
with the highest density in the case of complementary dot arrangement
(FIG. 5), or is a position with the lowest density in the case of dot
arrangement in the same position (FIG. 6). When a required alignment
resolution is on the order of relative printing position shifting unit of
the alignment pattern group, an adjusting value may be determined based
on the position shifting amount xi of patterns aligned best in the
alignment pattern group. When a resolution higher than the above is
required, an approximate curve representing a continuous density
distribution is firstly obtained based on the relationship between the
relative position shifting amount xi of the alignment patterns and the
density, and then an adjusting value for best aligned patterns is
obtained.

[0068] In order to obtain a continuous density distribution for shifting
amounts xi of a relative positions, an approximate curve is calculated
from density data of each pattern. A function determined as an
approximate curve is aimed at calculating a shifting amount xi of a
relative position at which a density distribution attains its peak, so
that it is only necessary that a density distribution can be reproduced
for shifting amounts of relative positions within a certain range from
the peak of the density distribution. Therefore, certain density data
which are within a range of shifting amounts of relative positions
reproducible by an approximate curve are extracted and thereby used. A
parameter for determining an approximate curve is determined from the
density data thus extracted, and an adjusting value is determined from a
shifting amount of a relative position corresponding to a peak position
of the curve.

[0069] The printing apparatus stores therein an adjusting value to control
timing of one of two printing operations as targets of a registration
process to align printing positions of the two printing operations. When
updating is not necessary to the adjusting value, a default value of the
adjusting value may be determined in a process of inspection at the time
of factory shipping, and the ROM 101 storing the default value may be
mounted on the printing apparatus. However, when a registration process
is performed by a user's instruction or by a service person, or when it
is hand-carried to a service center to be performed, the adjusting value
is stored in an EEPROM 110 to enable an update as needed. In this case,
an alignment pattern is printed with timing of one printing operation
controlled or shifted based on an adjusting value stored in the printing
apparatus to obtain information of the timing of a printing operation
that achieves the smallest relative position misalignment among elements.
When the smallest misalignment is obtained among printed alignment
patterns, information of timing of a printing operation is obtained.
Further, based on the timings of printing the alignment patterns, and the
timing of the printing operation that achieves the smallest relative
position misalignment, a new adjusting value is determined and stored in
the EEPROM 110. In any case, the adjusting value is referred as a
printing timing correction value at the time of printing of an image.

[0070] The magnitude of a change of density of an alignment pattern with
respect to a shifting amount of a relative position is varied depending
on an ink for printing an alignment pattern, a printing method, a
printing medium, or the like, but a correlation of a density to an area
factor is not supposed to be changed. However, when the shape of a
density distribution measured by the optical sensor 30 in practice does
not show a monotonic change to a change of an area factor, it can be said
that density data have changed due to a disturbance. When an influence
from a disturbance is large as described above, an alignment pattern
exhibiting the foregoing maximum density, or a peak position of a density
distribution curve does not match a position at which an actual amount of
misalignment of a relative position becomes minimum. In order to exclude
this influence, there is a method in which as in Japanese Patent
Application Laid-Open No. 2006-102997, density data of an alignment
pattern influenced by a disturbance are not used at the time of
calculation of an adjusting value, and in which a pattern to correct a
change of density caused by a disturbance is simultaneously printed.

Embodiment of Calculation Method of Alignment Value

[0071] In this embodiment, however, as a calculation method of an
adjusting value, used is a method in which a change of density with
respect to a shifting amount of a relative position is obtained from an
alignment pattern as a density curve. For density data to be used for
determining this density curve, used are only points in a range in which
a curve and a density data distribution are consistent with each other to
a large degree. This is more desirable to obtain the position of a peak
of a density distribution with high accuracy. However, an excessive
limitation on density data to be used causes the density data to be more
influenced by a change of density data stemming from a disturbance. Thus,
reliability of density data is determined by using a method to be
described later for measuring an impact of a disturbance on density data,
and when the reliability is high, a range of density data to be used for
a calculation of an adjusting value is narrowed, and when the reliability
is low, the range of density data is widened. In this manner, a change of
density with respect to an area factor made relatively larger than a
change caused by a disturbance checks a deterioration of an accuracy of
determination of an adjusting value is checked.

[0072] More specifically, in this embodiment, reliability can be
determined by using the following three methods.

First Reliability Determination Method

[0073] A change of density with respect to a shifting amount of a relative
position of alignment patterns can be predicted from a change of density
with respect to a change of an area factor. As an area factor increases,
density increases, and as the area factor decreases, density decreases.
In other words, for an alignment pattern in which printing positions of
two alignment pattern elements of the alignment pattern are best aligned
in a group of the alignment patterns, density becomes maximum in the case
of FIG. 5 (minimum in FIG. 6). As a shifting amount of a relative
position increases, density is expected to decrease in FIG. 5 (increase
in FIG. 6).

[0074] The magnitude of a change of density with respect to a shifting
amount of a relative position of alignment patterns varies depending on
inks with which an alignment pattern is printed, a printing method, a
printing medium, and the like, but a slope of a change of density with
respect to a change of an area factor is expected to remain unchanged. In
addition, each shifting amount of a relative printing position of a
second alignment pattern element with respect to a first alignment
pattern element is a predetermined value. However, the shape of a density
distribution actually measured by the optical sensor 30 sometimes shows
that there is no monotonic change to a shifting amount of a relative
printing position. In this case, it is considered that a variation has
occurred in density data since a printing position is different from a
supposed position due to a disturbance, or since a correct reading of the
density of the alignment pattern cannot be made using the optical sensor
30 at the time of a measurement of the density. As described above, when
an influence of a disturbance is large, reliability of density data is
judged to be low.

Second Reliability Determination Method

[0075] In a calculation of an adjusting value, a density curve is obtained
in a range of data having a high reliability. As described above, the
data are those extracted in a range in which extracted data are quite
consistent with an approximate curve of a change of density with respect
to a shifting amount of a relative position. When a correlation between
the density data and the curve is deteriorated in this range, it may be
considered that a variation due to a disturbance is large. A standard
deviation as a parameter indicating the correlation between the density
data and the curve, and a threshold value of the standard deviation are
set, the standard deviation being obtained from the density data and the
curve, and the threshold value being one in which an adjusting value does
not greatly vary due to a disturbance. When the density data has a
standard deviation not less than the threshold value, it is determined
that an influence of a disturbance on a change of density is large in the
range of the data so that the reliability of the density data is low.

[0076] The parameter indicating a correlation between the density data and
the density curve to be used in the second reliability determination
method may be one other than the standard deviation. For example, by use
of even a coefficient of correlation, a variance, or the like, it is
possible to determine whether there is a certain correlation between
density data and a density curve.

Third Reliability Determination Method

[0077] As describe above, the magnitude of a change of density with
respect to an area factor varies depending on inks with which an
alignment pattern is printed, a printing method, a printing medium, and
the like. For example, when an optical characteristic of an alignment
pattern printed with a light-color ink is measured by an optical sensor,
a difference between densities of respective alignment patterns becomes
smaller compared with one in the case of other inks. Furthermore, a
density detected and the degree of an influence of a disturbance on the
density vary depending on optical characteristics of an LED and a
photodiode to be used for measurement. Therefore, the reliability of
density data is determined to be low, in the case of using a printing
method or an optical measuring method of an alignment pattern, or a
combination of these methods in which: a change of density showing a
shifting amount in a relative position is not sufficiently large; and the
density data is largely influenced by a disturbance. For example, when an
ink with an optical characteristic of the color that is difficult to
measure is used for the printing of the alignment pattern, the
reliability of density data is determined to have a low reliability.

[0078] Moreover, the second and third reliability determination methods
are combined and can be adopted as a single reliability determination
method. That is, a determination as to whether density data and a density
curve exhibit a correlation to a certain degree or higher is performed
for each different printing method or for each optical measuring method.
For example, a threshold value of a standard deviation at which an
adjusting value does not greatly vary due to a disturbance is set for
each ink color, and the threshold value is set low for an ink color
having a low reliability.

Combination of Reliability Determination Methods

[0079] In this embodiment, the first, second, and third reliability
determination methods of density data are combined for use as needed.
Since the third reliability determination method depends on adjustment
items of a registration, a calculation method may be determined in
advance. The first determination method can be applied in a stage of
optical characteristic is measured. The second determination method can
be applied in a stage in which a density curve is determined from density
data. As can be seen from the above, since the determination methods are
different from each other, two or more determination methods can be
combined as needed. For example, in a process procedure such as one shown
in FIG. 7, use of combined determinations enables calculation of an
adjusting value.

Example of Calculation of Alignment Value

[0080] More specifically, an aspect of an application of the reliability
determination methods to density data is described. As shown graphs (C1),
(D1) and (E1) in FIG. 8 as examples, density data with respect to
shifting amounts of relative positions are described. For the density
data, an adjusting value is obtained along a process of a reliability
determination process shown in FIG. 7.

[0081] First, seven alignment patterns whose shifting amounts of relative
printing positions of second alignment pattern elements relative to first
alignment pattern elements differ from each other are printed in Step S1
of FIG. 7 and, thereafter, optical characteristics of the seven alignment
patterns are measured by the optical sensor 30 in Step S2. It is
determined (Step S3), by the third reliability determination method,
whether density data obtained by measuring the alignment patterns by use
of the optical sensor is reliable, based on inks used for printing, an
LED, a printing medium, and the like. It is assumed that the density data
of FIG. 8 are determined to be reliable.

[0082] Subsequently, the second reliability determination method is
applied to determine (Step S4) whether density data change monotonically
in the shifting range of the relative printing position. The shifting
amount of the relative printing position herein represents a shifting
amount of printing position from a state there is no position
misalignment between two alignment pattern elements. In (C1) and (E1) in
FIG. 8, the density changes monotonically from its peak. However, the
density of (D1) in FIG. 8 does not change monotonically, and there are
data in which density is extremely deviated. Therefore, the density data
of (D1) in FIG. 8 are determined to be not reliable.

[0083] The data of (C1) or (E1) in FIG. 8, whose reliability has not been
determined to be low, is used for obtaining an approximate curve
expressing a change of density. Density data to be used for calculating
this approximate curve are only those of five alignment patterns, each
data being within a certain range from a peak as shown in FIG. 8 (Step
S5). Approximate curves obtained for each data of (C2) and (E2) in FIG. 8
are shown in dashed lines. Density data used are shown by black circles.
An application of the first determination method makes it clear that the
density data of (E2) in FIG. 8 does not have good correlation with the
approximate curve corresponding thereto while the density data of (C2) in
FIG. 8 has good correlation with the approximate curve corresponding
thereto. Therefore, the approximate curve of (E2) in FIG. 8 has not
reproduced the change of density and, therefore, the reliability of this
density data is determined to be low (Step S6).

[0084] Concerning the density data of (C2) in FIG. 8 whose reliability has
been determined to be high in accordance with the processes performed so
far, a shifting amount of a relative position at the peak position of
approximate curve of data of the five alignment patterns is calculated.
This shifting amount is decided as an adjusting value, and is stored.

[0085] In the cases of the pieces of density data of (D1) and (E1) in FIG.
8 whose reliabilities have been determined to be low by the application
of the above-described methods, these data pieces are processed in Step
S7. Here, in order to reduce the influence of a disturbance on the change
of density, a range of data used for calculating an approximate curve is
increased more than the range for highly reliable data, and data of seven
alignment patterns are used. An adjusting value is determined from a peak
position of the approximate curve indicated by a solid line which is
determined from density data of the range thus increased.

[0086] In this embodiment, when reliability is determined by the second
reliability determination method, among data of seven alignment patterns,
those of five alignment patterns each of which is within a certain range
from a density peak are used. That is, the second reliability
determination method is applied to these five pieces of data, and when
reliabilities are confirmed on the determinations of all these data
pieces, an adjusting value is finally determined based on approximate
curves of the five pieces of data. Meanwhile, when it is confirmed that
an application of any one of the third, first, and second determination
methods to these five data pieces does not show their reliability, a
range of the density data to be used for the calculation of an
approximate curve is increased, and an adjusting value is determined
based on an approximate curve as to data pieces of the seven alignment
patterns. That is, data pieces of five points are used when the
reliability is determined to be high, while data pieces of seven points
are used when the reliability is determined to be low. An approximate
curve is fitted to the data pieces, thereby, a standard deviation of data
from a function of the approximate curve becomes small, so that an
accuracy of an adjusting value can be improved. Accordingly, when there
is substantially no influence of a disturbance and when data are
reliable, only the obtaining of an approximate curve for the five
alignment patterns enables a quick and accurate determination of an
adjusting value, so that a registration process is quickly performed.
Meanwhile, when there is an influence of a disturbance, an adjusting
value is determined based on an approximate curve as to data pieces of
seven alignment patterns and, thereby, the influence of the disturbance
is avoided as much as possible, so that an accurate adjusting value can
be obtained.

[0087] In addition, in the processes of this embodiment, before
determination of reliability, seven alignment patterns are printed in
advance in Step S1 of FIG. 7. Here, a peak position of the density may be
calculated firstly, and data pieces of five alignment patterns which are
within a certain range from the density peak may be used so that they can
be provided for determinations in the third, first, and second methods.

[0088] Further, in Step S1, instead of seven alignment patterns within a
wide range, for example, five alignment patterns within a narrow range
may also be printed so that they can be provided for the above third,
first, and second reliability determinations. When it is determined that
the data does not have reliability in any one of the determinations, two
more alignment patterns may be added and printed to newly obtain an
approximate curve so that an adjusting value can be determined. However,
this embodiment is more advantageous than the above in points that
variation of the densities is possibly reduced and that the throughput of
a registration process can be improved, and so on, since alignment
patterns are printed at one time and, therefore no additional alignment
pattern is printed after a certain time period.

[0089] In addition, the foregoing descriptions are only examples: the
number of alignment patterns to be printed, or the number of alignment
patterns or the number of pieces of density data to be used at in the
beginning of reliability determination, and further, the number of pieces
of density data which is increased to obtain an approximate curve in
accordance with a result of a reliability determination, and the like;
and the number thereof can naturally be any suitable one.

Second Embodiment

[0090] Next, other embodiment to which the reliability determination is
applied is described.

[0091]FIG. 9 shows procedures of processes of the determining reliability
and the obtaining of an adjusting value in a second embodiment of the
invention. In this embodiment, two groups of alignment patterns can be
printed, and a second group of alignment patterns is printed in
accordance with the reliability of data of a first group of alignment
patterns. The first group of alignment patterns is for a coarse alignment
satisfying an alignment range required for a mechanical tolerance of a
printing apparatus. Meanwhile, the second group of alignment patterns, a
unit of shifting of a relative printing position between alignment
pattern elements is set smaller than that for the first group of
alignment patterns so as to have a high accuracy of an alignment. In the
first embodiment, as a result of a reliability determination, when the
obtaining of an adjusting value with high accuracy and with less
influence by a disturbance can be expected, a range of density data to be
used is limited and, thereby an accuracy of an adjusting value is
improved. In contrast, in the second embodiment, as a result of a
reliability determination, when it is determined that an influence of a
disturbance on an adjusting value is small, the second group of alignment
patterns having a smaller unit of shifting than the first group of
alignment patterns is used to obtain an adjusting value so that an
accuracy of an adjusting value is intended to be improved.

[0092] Additionally, dot dispositions may be different between the first
and second groups of alignment patterns, and a range of shifting of a
relative printing position between alignment pattern elements in the
second group of alignment patterns may also be narrower than that of the
first group of alignment patterns.

[0093] An object of use of the second group of alignment patterns is, when
a characteristic of density data obtained by the optical sensor 30 is
favorable, to determine an adjusting value by use of a second group of
alignment patterns having a higher accuracy than the first group of
alignment patterns. Further, when the reliability of density data of the
first group of alignment patterns is low and when an improvement of the
accuracy cannot be expected in a combination of printing methods because
of an influence of a disturbance, the second group of alignment patterns
is not printed in the same combination of the printing methods.
Accordingly, the shortening of alignment time and the saving of printing
media can be achieved.

[0094] Now, with reference to FIG. 9, a group of alignment patterns (a
first group of alignment patterns) is printed (Step S11) on a printing
medium as in the first embodiment, and an optical characteristic is
measured (Step S12) by the optical sensor 30. Subsequently, after a
density peak calculation (Step S13), the third and first reliability
determinations which are the same as those described above are further
performed (Steps S14 and S15). When there is no missing data in the third
and first reliability determinations, the second reliability
determination does not need to be performed.

[0095] When density data of the first group of alignment patterns
determined to be reliable by the third and first reliability
determinations, it is considered that the data is hard to be influenced
in the printing methods of this combination, so that the second group of
alignment patterns is, further, printed on a printing medium (Step S16).
An optical characteristic of the second group of alignment patterns is
also similarly measured by the optical sensor 30. In addition, density
data are extracted in the same manner as described above, and an
approximate curve is obtained from this density data, so that reliability
of the second alignment pattern is determined by the second reliability
determination method (Steps S17 and S18). Incidentally, prior to this
process, the third reliability determination may be applied.

[0096] When the second alignment patterns are determined to be reliable,
an adjusting value is calculated based on a peak position of an
approximate curve which is obtained from density data extracted from the
second alignment patterns, and then is stored in the printing apparatus
(Step S19). Meanwhile, in the reliability determination having been
performed so far, when the reliability of density data of the first
alignment pattern is determined to be low (when a negative determination
is made in Step S14 or S15), an adjusting value is calculated based on an
approximate curve obtained from the extracted density data of the first
alignment patterns, and then is stored in the printing apparatus.
Further, also when the reliability of density data of the second
alignment pattern is determined to be low (when a negative determination
is made in Step S18), an adjusting value is calculated based on an
approximate curve obtained from the extracted density data of the first
alignment patterns, and then is stored in the printing apparatus.

[0097] Incidentally, also in this embodiment, a range of density data to
be used may naturally be increased depending on a result of a reliability
determination.

Other

[0098] The configurations and the numbers of the above-described arrays of
ejection openings and of print heads are simply examples, and further,
the types, the numbers, and the like of the above-described ink color
tones are also examples. Therefore, for all described above, any suitable
ones may be adopted. For example, in the above-described examples, the
single print head is configured so that total of two arrays, one for a
black ink and the other for color (C, M, Y) inks, of ejection openings
are provided to the print head. However, two or more arrays of ejection
openings may be provided for the same color tone, or one or more arrays
of ejection openings may be provided for each color tone. Further, the
number of array of ejection openings provided to a single print head, or
the number of print heads may suitably be determined. In addition, the
invention is effective not only for a relationship between arrays of
ejection openings, but also for a registration process in a case of
bi-directional printing by use of the same array of ejection openings. In
that sense, the configuration of the invention may also be one including
only a single array of ejection openings.

[0099] In each of the above-described embodiments, description has been
given to the case where the invention is applied to an inkjet printing
apparatus which forms an image on a printing medium by ejecting inks onto
the printing medium from a print head. However, the invention is
applicable to any type of printing apparatus so long as it forms dots to
perform printing while moving a print head and a printing medium
relatively to each other.

[0100] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0101] This application claims the benefit of Japanese Patent Application
No. 2007-205911, filed Aug. 7, 2008, which is hereby incorporated by
reference herein in its entirety.